System designs are routinely constrained by a limited number of power supply voltages. As an example of such a system design, consider a conventional battery powered notebook computer. For proper operation, components of the computer including display, processor, and memory employ several technologies and consequently require power to be supplied at several voltages. The design, therefore, includes power conversion circuitry to efficiently develop voltages in some cases having magnitudes outside the range from zero to the battery voltage or in another case a voltage of reverse polarity. One such power conversion circuit is known as a charge pump.
The demand for high efficiency charge pump circuits has increased with the increasing number of applications for battery powered systems such as notebook computers, portable telephones, security devices, battery backed data storage devices, remote controls, instrumentation, and patient monitors, to name a few.
Inefficiencies in conventional charge pumps lead to reduced system capability and lower system performance. Examples of system capabilities that are adversely affected by such inefficiencies include limited battery life, excess heat generation, and high operating costs. In non-battery operated applications, the latter two limitations also apply. Examples of lower system performance include low speed operation, excessive delays in operation, loss of data, limited communication range, and the inability to operate over wide variations in ambient conditions including ambient light level and temperature.
Conventional pump circuits are characterized by a two part cycle of operation and low duty cycle. Pump operation includes pumping and resetting. Duty cycle is low when pumping occurs at less than 50% of the cycle. Low duty cycle consequently introduces low frequency components into the output DC voltage provided by the pump circuit. Low frequency components cause interference between portions of a system, intermittent failures, and reduced system reliability. Some systems employing conventional pump circuits include filtering circuits at additional cost, circuits to operate the pump at elevated frequency, or both. Elevated frequency operation in some cases leads to increased system power dissipation with attendant adverse effects.
In addition to constraints on the number of power supply voltages available for system design, there is an increasing demand for reducing the magnitude of the power supply voltage. The demand in diverse applications areas could be met with high efficiency charge pumps that operate from a supply voltage of less than 5 volts.
Such applications include memory systems backed by 3 volt standby supplies, processors and other integrated circuits that require either reverse polarity substrate biasing or boosted voltages outside the range 0 to 3 volts for improved operation. As supply voltage is reduced, further reduction in the size of switching components paves the way for new and more sophisticated applications. Consequently, the need for high efficiency charge pumps is increased because voltages necessary for portions of integrated circuits and other system components are more likely to be outside a smaller range.
In view of the problems described above and related problems that consequently become apparent to those skilled in the applicable arts, the need remains, in methods for supplying power to a circuit and particularly in systems including pumped power supplies, for alternatives to the conventional pump circuit having low efficiency, low duty cycle operation, and only practically operable from voltages of 5 volts and above.